Studded heat exchanger tubes



Nov. 4, 1969 H. F. STRAIGHT, JR, ET AL STUDDED HEAT EXCHANGER TUBESFiled June so. 1967 v44 4 W'fivsmoas r4. Kalle me m ATTORNEY UnitedStates Patent 3,476,180 STUDDED HEAT EXCHANGER TUBES Harry F. Straight,Jr., Succasunna, and John A. Kivlen,

Sparta, N.J., assignors to Esso Research and Engineering Company, acorporation of Delaware Filed June 30, 1967, Ser. No. 650,474 Int. Cl.F28f 1/20 US. Cl. 165-172 5 Claims ABSTRACT OF THE DISCLOSURE Heatexchange tubes having extended surface studs about approximatelyone-half of the tube periphery are compactly arranged in a furnaceconvection section to provide effective heat transfer capacityapproaching heat transfer capacity of fully studded tubes.

DESCRIPTION OF THE INVENTION This invention relates in general tofurnaces, and in particular to improvements in extended surface tubestherefore permitting the contruction of a furnace heat exchanger whichis smaller in size and lower in cost than conventional furnace heatexchangers employing prior art extended surface tubes.

In convection sections of conventional furnaces, either of the steamboiler or of the process furnace type used in the petroleum and chemicalindustries, it has been conventional practice to extend the surface areaof the heat exchange tubes running therethrough by applying as many aspossible studs to the outer surface thereof. The studding of tubes inthe conventional manner, while greatly increasing their effectivesurface area and their corresponding heat transfer capacity,nevertheless, adds substantially to their cost and also to theireffective outside diameter. The enlarging of the effective tube diameternecessitates the increase in spacing between tube centers, resulting inan overall increase in the size of the heat exchange enclosure. Inaccordance with the present invention, it has been discovered thatsubstantially fifty percent of the studs may be eliminated from theportion of the tube periphery furthest most from the source of heat oron the downstream side of the flow of hot gases without substantiallyreducing the heat transfer capacity of the studded tube. The omission ofthe studs from the, so to speak, backside of each tube periphery permitsthe placement of the tube centers closer together, with the result thata smaller furnace enclosure may be constructed having the same number ofheat exchange tubes running therethrough to thereby produce asubstantial cost saving. In one form of the invention wherein the tipsof the studs of one tube were positioned to lie within the studfree zoneof an adjacent tube, it has been possible to construct a convectionsection of a furnace having ninety to ninety-five percent of the heattransfer capacity with only approximately fifty percent of the extendedsurface of a prior art convection section using fully studded tubes. Inaddition, the closeness an the effect of the overlying relationship ofthe studs on one tube with the studs on the adjacent tube create aninter-acting turbulence or scrubbing of the hot gases passing thereoverto enhance the heat transfer efiiciency of the studs over similar studsin a non-overlying relationship.

Accordingly, it is an object of the present invention to provide alow-cost, extended surface heat exchanger tube, having substantiallyninety to ninety-five percent of the efficiency of prior art fullystudded tubes, yet employing only about fifty percent of the studsformerly employed.

Another object of the invention is to provide a tube studdingarrangement wherein overlapping and a highly compacted tube arrangementis possible.

"ice- Another object of the invention is to provide a low cost highefficiency convection section for a furnace.

These and other objects of the invention will become apparent and theinvention will be fully understood from the following description anddrawings in which:

FIG. 1 is a diagrammatic view of a typical cabin type process furnace;

FIG. 2 is a cross-sectional view of several heat exchange tubes inaccordance with the invention; and

. FIG. 3 is a side elevation view of a single tube of the invention.

It will be understood that the drawings represent merely arepresentative embodiment of the invention and that other embodimentsare contemplated within the scope and claims hereafter set forth.

Referring to the drawings in particular, a conventional cabin heater 10is diagrammatically shown having a plurality of up-firing burners 24located along a bottom wall thereof. The burners 24 discharge combustionproducts upwardly to heat a plurality of primary heat transfer tubes 16in the lower radiant heat section 12 of the furnace. Thereafter, the hotproducts of combustion continue their upward travel into a conventionalconvection or economizer section 14 thereabove which includes aplurality of transversely extending secondary heat transfer tubes 18 andoutwardly through an uppermost flue 26. Each of the tubes 18 includes aplurality of headed studs 20 which are attached in rows in staggeredfashion typically by welding at their base directly to the outer surfaceof the tube 18. The studs 20 include enlarged base portions and arepreferably located relatively close together over approximately of thetube pheriphery. The tube centers are located and positioned by suitablemounting structure not shown located in the side walls of convectionsection 14 in such a manner as to place the tips of the studs on onetube within the stud-free zone of an adjacent tube. This relationship ofadjacent tubes on one horizontal layer to the stud-free zone on thetubes below it on the next horizontal layer permits closer horizontalspacing of adjacent layers as well as closer side-by-side spacing oftubes on the same layer due to the fact that clearance need notbeprovided between stud tips but only between a tube periphery which isstud-free and the adjacent stud tips. This relationship may best be seenat the spacing gap 22 of FIG. 2 wherein it may be readily appreciatedthat a substantial space economy has been effected by the omission ofstuds from the tube periphery from the two lowermost tubes at this pointto permit the close positioning of the center and uppermost tube. Itwill be understood that in FIG. 2 the flow of hot heating gases isupward from the bottom of the figure to the upper portion of the figureso that essentially all of the studs look toward, rather than away from,the source of heat. In FIG. 2, as described above, the inventiveomission of the nonessential studs from the backside of the tubeperiphery permits the substantial reduction in the vertical tube spacingbetween tube centers designated by the arrow A, as well as a substantialreduction in horizontal tube spacing between centers designated by thearrow B.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the inventiveprinciples, it will be understood that the invention may be embodiedotherwise and applied to numerous types of heating devices other thanconvection sections of furnaces without departing from the inventiveprinciples. For instance, the invention is equally adaptable toeconomizers of steam power boilers, as well as other typical heatexchange equipment where it is desirable to obtain maximum heat transferat the lowest possible cost of enclosure as well as tube cost.

What is claimed is:

1. In a heat transfer section of a furnace, a flue for heating gases;and a plurality of heat exchanged tubes arranged transversely of theflow of heating gases, each of said heat exchange tubes including aplurality of individual extended surface metallic studs welded theretoand positioned in staggered rows about approximately 190 of the tubeperiphery leaving the remaining tube periphery free of studs, and meansfor mounting adjacent tubes in said flue in compacted relationshipwherein the tips of the studs on one tube lie within the stud-free zoneof an adjacent tube.

2. In a heat transfer section of a furnace, a flue for heating gases;and a plurality of horizontal layers of heat exchange tubes arrangedtransversely of the flow of heating gases, each of said heat exchangetubes in each layer including a plurality of individual extended surfacemetallic studs welded thereto and positioned in staggered rows aboutapproximately 190 of the tube periphery leaving the remaining tubeperiphery free of studs, and means for mounting tubes in one layerpartially in the fiow shadow of the tubes in the adjacent layer incompacted relationship therewith wherein the tips of the studs on onetube lie within the stud-free zone of an adjacent tube on the adjacentlayer.

3. The combination in accordance with claim 2, wherein the end of eachof said studs that is welded to said tube is substantially larger indiameter than the remaining diameter of said studs.

4. Apparatus comprising, in combination, a fiue for the passage ofheated flowing gases therethrough, a plurality of metallic tubes, eachtube including a plurality of individual extended surface circularmetallic studs welded thereto and positioned in staggered rows aboutapproximately 190 of the tube periphery leaving the remaining tubeperiphery free of studs, means mounting each of said tubes in said fluewith its studs oriented to face upstream of said flowing gases in aplurality of layers with the tubes in one layer partially in the flowshadow of the tubes in the adjacent layer and in compacted relationshiptherewith, wherein the tips of the studs on one tube lie within thestud-free zone of an adjacent tube on the adjacent layer.

5. The combination in accordance with claim 4, wherein the end of eachof said studs that is welded to said tube is substantially larger indiameter than the remaining diameter of said studs.

References Cited UNITED STATES PATENTS 1,390,783 9/1921 Hering 165l1,521,864 1/1925 Broido 122367 XR 1,942,211 1/1934 Hartwig 122-367 XR3,163,153 12/1964 Grilfin 122--356 XR FOREIGN PATENTS 545,608 6/ 1942Great Britain.

743,795 1/ 1933 France.

827,519 1/1938 France.

FRED C. MATTERN, 111., Primary Examiner MANUEL ANTONAKAS, AssistantExaminer US. Cl. X.R. l22367; 165-181

